Identification of an immunodominant CD4+ T cell epitope in the VP6 protein of rotavirus following intranasal immunization of BALB/c mice

The only lymphocytes required for protection against fecal rotavirus shedding after intranasal immunization of BALB/c (H-2d) mice with a chimeric rotavirus VP6 protein (MBP∷VP6) and the mucosal adjuvant LT(R192G) are CD4+ T cells. The purpose of this study was to identify CD4+ T cell epitopes within VP6 that might be responsible for this protection. To make this determination, spleen cells obtained from BALB/c mice following intranasal immunization with MBP∷VP6/LT(R192G) were stimulated in vitro with either MBP∷VP6 or overlapping VP6 peptides containing ≤ 30 amino acids (AA). The numbers of memory (CD44high) CD4+ T cells stimulated to produce TH1 and TH17 cytokines (IFNγ and IL-17), as well as the quantities of these cytokines released into the cell supernatants, were then measured relative to those produced in mock-stimulated cells from the same animals. One epitope expected to be found was the VP6 14-mer AA289–302, previously identified as a CD4+ T cell epitope in H-2d mice. This was not observed but instead the only VP6 epitope identified was AA242–259, the dominant CD4+ T cell epitope previously reported after oral, live rotavirus immunization.